diff --git a/src/xdiff/xmacros.h b/src/xdiff/xmacros.h
index f58cf08..028ca6e 100644
--- a/src/xdiff/xmacros.h
+++ b/src/xdiff/xmacros.h
@@ -24,7 +24,7 @@
 #define XMACROS_H
 
 
-#ifdef __hpux
+#if defined(__hpux) || defined(VMS)
 # ifndef SIZE_MAX
 #  define SIZE_MAX ((size_t)(-1))
 # endif